This invention pertains to radio frequency transceivers and, in particular, to a method and a system that uses very short pulses of electromagnetic energy, e.g., an ultra wideband signal, to detect the position of one or more objects. The invention may be used in radar applications for determining the position of passively scattered objects, and also in ranging applications for determining the distance between two appropriately configured, cooperating transponder units.
Much work has been done in recent years on the use of very short pulses of radio frequency or microwave energy for radar applications. For example, McEwan (U.S. Pat. No. 5,986,600) describes a Doppler radar with an oscillator that is turned on and off by separate control signals, and with a range gating function determined by the duration of the oscillation. In another patent, McEwan (U.S. Pat. No. 6,191,724) describes a system which is based upon the use of pulse-echo techniques, and which also employs range-gating techniques in order to build up information about scattered targets at different locations. In McEwan (U.S. Pat. No. 6,137,438), the use of equivalent time techniques is described wherein many such transmit pulses are needed in order to resolve the position of a given passive target.
In each of the above examples, a transmitted pulse is utilized only for a specific, narrow range excursion (i.e., a xe2x80x9crange binxe2x80x9d) and requires the transmission of multiple pulses to accumulate data covering all range bins of interest.
In another set of applications, the precise location (geolocation) of a transponder is determined by time-of-flight measurements. Fontana (commonly-owned U.S. Pat. No. 6,054,950, incorporated herein), for example, describes a system wherein time-difference of-arrival measurements are made from a set of fixed transceiver at known locations. Position information is then obtained from calculations based on these measurements. Since the system is based on time-differences-of-arrival, it is necessary to have two or more transceivers at known locations in order to deduce position information for a transponder. That is, some form of infrastructure is needed to establish the position of the transponder even if only relative position information is required.
In accordance with one aspect of the present invention, there is provided a transceiver to ascertain distance of a object comprising a generator to produce a trigger signal, e.g., a clock signal, a transmitter that transmits a nanosecond pulse in response to the trigger signal, a receiver including a pulse detector to detect return signals, a shift register that samples return signals during multiple time-shifted periods, and a controller that obtains data samples from respective cells of the shift register to ascertain distance of the object based on the number of shifts from an occurrence of the trigger signal. Preferably, a system clock produces periodic trigger signals and a high-speed clock synchronized with the system clock drives the shift register.
In another embodiment, a second shift register is provided to sample time-delayed return signals and the controller obtains data samples from the second shift register to provide increased resolution of distances or times of receipt of the return signals.
In addition, the invention also includes a method of determining distance of multiple scattered objects comprising the steps of producing a trigger signal, transmitting an RF pulse in response to the trigger signal, detecting return signals produced by reflections of the RF pulse, sampling object return signals during multiple time-shifted intervals starting from an initial occurrence of the trigger signal in order produce data samples, and ascertaining the distance of multiple scattered objects based on the number of time-shifted intervals of detected pulses from the occurrence of the trigger signal. Preferably, the trigger signal is generated in the form of a clock signal, the RF pulse is a nanosecond pulse, and a high-speed clock synchronized with the clock signal effects step-wise sampling during time-shifted intervals.
In another aspect of the invention, there is provided a system to determine a distance between participating objects having cooperating transceivers, e.g., transponders, wherein the system comprises first and second transceivers respectively associated with the participating objects; each transceiver including a system clock to produce a local clock signal, a transmitter that transmits a nanosecond pulse according to the clock signal, a local receiver including a detector that detects a nanosecond pulse transmitted by the other transceiver, a local shift register that samples the presence of a nanosecond pulse during respective timing intervals defined by a high-speed clock that is synchronized with the local system clock; and the second transceiver has a controller that accesses the local shift register thereof to ascertain a first offset measurement of a first packet sent by the first transceiver; and the first transceiver has an associated controller that accesses the local shift register thereof to ascertain a second offset measurement of a second packet sent in response to receipt of the first packet by the second transceiver, wherein the second packet includes information indicative of the first offset measurement, and wherein the associated controller ascertains inter-object distance based on a relationship among offset measurements, clock skews, and propagation time. In another embodiment, the shift register is augmented with a matrix having rows indicative of data samples of the shift register observed during respective intervals defined by the system clock wherein successive rows of said matrix comprising information indicative of the first offset measurement. Further, an identification code may be included in the information.
In yet another embodiment of the invention, a method of determining distance between participating objects comprises the steps of providing first and second transceivers respectively associated with the participating objects, at the first transceiver, transmitting a nanosecond pulse according to a local clock signal; at the second transceiver, detecting the nanosecond pulse transmitted by the first transceiver, producing data samples by sampling a presence of the transmitted nanosecond pulse during respective timing intervals defined by a high-speed clock synchronized with the local clock signal, and accessing the data samples to ascertain a first offset measurement relative to a system clock signal of a first packet sent by a first transceiver; and at the first transceiver, producing data samples by sampling for a presence return signals and accessing the data samples to ascertain a second offset measurement relative to a system clock of a second packet sent in response to receipt of the first packet by the second transceiver, the second packet including information indicative of the first offset measurement, and ascertaining inter-object distance based on a relationship among offset measurements, clock skew, and propagation time. A relationship between or among other parameters may also be used to determine inter-object distance. The method may further include providing a matrix of information bits samples during multiple system clock intervals thereby to provide a way to extract payload information, such as an identification code or other information, e.g., navigation, geo-positioning, or other information to be communicated between or among participating objects.
In yet a further embodiment of the invention, there is provided a method of ascertaining distance or propagation time of a nanosecond pulse between participating objects wherein the method includes the steps of providing first and second transceivers respectively co-located with the participating objects, each transceiver having an associated pulse transmitter to transmit a nanosecond pulse, an associated detector to detect a nanosecond pulse, and an associated local shift register that samples an incoming signal the may include a nanosecond pulse sent by the other transceiver during successive shift intervals thereof; and utilizing predetermined circuit delays and position of sampled data in said shift register to ascertain distance or time of flight of a pulse between the participating objects.
Other aspects and embodiments of the invention will become apparent upon review of the succeeding description taken in conjunction with the accompanying drawings. The invention, though, is pointed out with particularity by the appended claims.